Synthesis of phosphonate derivatives of methylenecyclopropane nucleoside analogues by alkylation-elimination method and unusual opening of cyclopropane ring

Article abstract of DOI:10.1016/S0040-4020(02)00589-6

The synthesis of phosphonates of methylenecyclopropane nucleoside analogues 15a-18a, 15b-18b and 15c-18c by alkylation-elimination approach is described. In a foreshortened series, methanesulfonate 19 was transformed by Michaelis-Becker reaction with diethyl or diisopropyl phosphite to methylenecyclopropane phosphonates 20a or 20b. The latter were converted to vicinal dibromides 21a and 21b which were then used for alkylation-elimination of nucleic acid bases (adenine) or precursors (2-amino-6-chloropurine and N⁴-acetylcytosine). The intermediary Z+E-isomers 22a+23a and 22b+23b were dealkylated with bromo- of iodotrimethylsilane to free phosphonic acids 15a, 16a and phosphonate with an open cyclopropane ring 25 which were separated by ion exchange chromatography on Dowex 1. Phosphonate diesters 22c and 23c were separated by chromatography on silica gel, they were hydrolyzed to guanine derivatives 22d and 23d which were then dealkylated to give target analogues 15b, 16b and products of addition of hydrogen bromide or iodide across the double bond 26a or 26b. The E+Z-isomers 22e+23e were converted to cytosine phosphonates 15c+16c and cyclic phosphonate with an open cyclopropane ring 27a. In a homologous series of phosphonates, dibromocyclopropane 34 was converted to intermediate 31 by reaction with diisopropyl methyl phosphonate and subsequent β-elimination. Compound 31 was transformed to vicinal dibromide 36, a key component for alkylation-elimination of nucleic acid bases. The rest of the synthetic sequence followed the scheme described for the series of lower homologues to give the Z-isomeric phosphonates 17a, 17b, E-isomers 18a, 18b and E+Z-isomers 17c+18c as the final products. All methylenecyclopropane phosphonates were devoid of antiviral activity with the exception of guanine derivative 15b which inhibited the replication of varicella zoster virus (VZV) and it was non-cytotoxic.

Full text of DOI:10.1016/S0040-4020(02)00589-6

TETRAHEDRON
Pergamon
Tetrahedron 58 (2002) 6047±6059
Synthesis of phosphonate derivatives of methylenecyclopropane
nucleoside analogues by alkylation±elimination method and
unusual opening of cyclopropane ring
Hui-Ping Guan,a Yao-Ling Qiu,a Mohamad B. Ksebati,b Earl R. Kernc and Jiri Zemlickaa,p
aDevelopmental Therapeutics Program, Department of Chemistry, Barbara Ann Karmanos Cancer Institute,
Wayne State University School of Medicine, 10E. Warren Avenue, Detroit, MI 48201-1379, USA
bCentral Instrumentation Facility, Department of Chemistry, Wayne State University, Detroit, MI 48202, USA
cDepartment of Pediatrics, The University of Alabama at Birmingham, Birmingham, AL 35294, USA
Received 14 March 2002; revised 4 June 2002; accepted 6 June 2002
AbstractÐThe synthesis of phosphonates of methylenecyclopropane nucleoside analogues 15a±18a, 15b±18b and 15c±18c by alkylation±
elimination approach is described. In a foreshortened series, methanesulfonate 19 was transformed by Michaelis±Becker reaction with
diethyl or diisopropyl phosphite to methylenecyclopropane phosphonates 20a or 20b. The latter were converted to vicinal dibromides 21a
and 21b which were then used for alkylation±elimination of nucleic acid bases (adenine) or precursors (2-amino-6-chloropurine and
N4-acetylcytosine). The intermediary Z1E-isomers 22a123a and 22b123b were dealkylated with bromo- of iodotrimethylsilane to free
phosphonic acids 15a, 16a and phosphonate with an open cyclopropane ring 25 which were separated by ion exchange chromatography on
Dowex 1. Phosphonate diesters 22c and 23c were separated by chromatography on silica gel, they were hydrolyzed to guanine derivatives
22d and 23d which were then dealkylated to give target analogues 15b, 16b and products of addition of hydrogen bromide or iodide across
the double bond 26a or 26b. The E1Z-isomers 22e123e were converted to cytosine phosphonates 15c116c and cyclic phosphonate with an
open cyclopropane ring 27a. In a homologous series of phosphonates, dibromocyclopropane 34 was converted to intermediate 31 by reaction
with diisopropyl methyl phosphonate and subsequent b-elimination. Compound 31 was transformed to vicinal dibromide 36, a key compo-
nent for alkylation±elimination of nucleic acid bases. The rest of the synthetic sequence followed the scheme described for the series of lower
homologues to give the Z-isomeric phosphonates 17a, 17b, E-isomers 18a, 18b and E1Z-isomers 17c118c as the ®nal products. All
methylenecyclopropane phosphonates were devoid of antiviral activity with the exception of guanine derivative 15b which inhibited the
replication of varicella zoster virus (VZV) and it was non-cytotoxic. q 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction
Recently, we have described a new series of nucleoside
analogues where a furanose ring is replaced with methylene-
cyclopropane system. The purine Z-isomers 1a have a
broad-spectrum antiviral activity whereas pyrimidines or
E-isomers 2a are effective only exceptionally.1,2 Conversion
of purine analogues 1a or 2a to phosphoralaninate pro-
nucleotides 1b or 2b improved in many cases the antiviral
potency of less potent parent compounds.3 These results
have indicated that pronucleotides 1b and 2b are capable
of delivering the free monophosphates 1c and 2c into the
virus-infected cells. The latter metabolites are then
processed to the respective di- and triphosphates in a
manner similar to other nucleoside analogues.4
The transformation of parent analogues 1a and 2a to lipo-
philic pronucleotides 1b and 2b is just one strategy to intro-
duce phosphorylated metabolites into the virus-infected
cells. Alternately, it has been shown that phosphonate analo-
gues of nucleotides which are resistant to enzymatic dephos-
phorylation and able to penetrate cell membrane can
function as surrogates for the corresponding monophos-
phates. Several such phosphonates derived from furanose
or acyclic nucleoside analogues exhibited antiviral activity.
They can be divided into two classes: (i) `foreshortened'
phosphonates where the nucleic acid base is separated
Keywords: methylenecyclopropane nucleoside analogues; alkylation±elim-
ination; cyclopropane ring.
p
Corresponding author. Tel.: 11-313-833-0715x2452; fax: 11-313-832-
7294; e-mail: zemlicka@kci.wayne.edu
0040±4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(02)00589-6

6048
H.-P. Guan et al. / Tetrahedron 58 (2002) 6047±6059
from the phosphorus by a chain of four atoms (formula 3),
one atom shorter than in the respective nucleoside phos-
phates 4 and (ii) `full-length' analogues (formula 5) where
0
0
0
0
0
the ®ve-atom chain of nucleotides 4 (C1 ±O1 ±C4 ±C5 ±O5 )
is preserved. Examples of nucleoside phosphonates with
antiviral activity include foreshortened analogues5±8 6±8
as well as full-length derivatives7,9±13 9±14. Phosphonates
where the chain length between a heterocyclic base and
phosphonate moiety exceeds ®ve atoms14,15 or is shorter
than four atoms16 lack antiviral activity.
Therefore, it was of interest to investigate synthetic
approaches to methylenecyclopropane phosphonates 15±
18. For reasons mentioned above, both foreshortened (series
15 and 16) and full-length analogues (series 17 and 18) were
of interest. Although cyclopropane phosphonates17±20
including those comprising a nucleic acid base21,22 are
known, methylenecyclopropane phosphonates have not
been described to the best of our knowledge. Alkylation±
elimination approach which had been successfully exploited
for synthesis of methylenecyclopropane analogues of
nucleosides,1,2 was considered as a convenient strategy. A
key element in this method is the synthesis of an alkylating
agent comprising a preformed phosphonate moiety that
could serve for alkylation of a nucleic acid base or suitable
precursor.
2. Synthesis
A. Foreshortened phosphonates. For the synthesis of phos-
phonates 15 and 16 the known23 (methylenecyclopropyl)-
methyl methanesulfonate (19) served as a convenient
starting material (Scheme 1). The Michaelis±Becker reac-
tion of 19 with diethyl phosphite using NaH in THF gave
diethyl (methylenecyclopropyl)methyl-phosphonate (20a)
in 88% yield. In a similar fashion, diisopropyl phosphite
afforded phosphonate 20b (84%). Addition of bromine to
20a via pyridinium tribromide gave Z,E-dibromo phos-
phonate 21a in 96% yield. The latter intermediate was
used for alkylation±elimination procedure with adenine
using K2CO3 in DMF at 1108C to give a mixture of Z-
and E-isomers 22a123a (57%) and 9-ethyladenine (24,

H.-P. Guan et al. / Tetrahedron 58 (2002) 6047±6059
6049
Scheme 1.
28%) arising from a competitive ethylation with diethyl
phosphonate 21a. Similar side reaction was described in
alkylation of adenine with other dimethyl or diethyl
phosphonate derivatives24,25 but it was avoided by using
diisopropyl esters.25 Therefore, diisopropyl phosphonate
20b was transformed to dibromide 21b which was used in
situ for alkylation±elimination with adenine to give Z1E
isomeric mixture 22b123b in 69% yield. As expected, no
alkylated adenine was detected. Isomeric mixtures
22a123a or 22b123b were not separable on a silica gel
column. Therefore, the Z1E-isomers 22a123a were
dealkylated24 with Me3SiI in CHCl3 at 2408C to afford
free phosphonates which were separated by chromato-
graphy on Dowex 1 (formate) using formic acid as an
eluent. The Z-isomer 15a (17%) was eluted ®rst followed
by E isomer 16a (24%) and an unusual product of cyclo-
propane ring opening, phosphonate 25 (5%). Elution order
of both isomers is related to the distance between the phos-
phonate group and nucleic acid base. Thus, the Z (cis)
isomer is eluted faster than E (trans) isomer. A similar
elution pattern was observed26 for mixtures of ribonucleo-
tides (cisoid 50.transoid 20 or 30). Dealkylation of
22b123b followed by chromatography on Dowex 1
afforded the Z-isomer 15a (20%), E-isomer 16a (22%)
and the alkene derivative 25 (4%).
with 80% formic acid furnished guanine phosphonates
22d and 23d in virtually quantitative yields. Dealkylation
of the Z- and E-isomers 22d and 23d was performed using
Me3SiBr in DMF and the crude products were puri®ed by
chromatography on Dowex 1 (formate). Diisopropyl
Z-phosphonate 22d furnished the E,Z-bromo phosphonate
26a (10%) and Z-isomer 15b (58%). The side-product 26a
resulted from an addition of elements of HBr (generated
during dealkylation) across the double bond of methylene-
cyclopropane phosphonate 15b. An unsaturated derivative
with an open cyclopropane ring observed in case of adenine
phosphonates 15a and 16a (see compound 25) was not
isolated. In a similar fashion, the E-phosphonate 23d
afforded compound 26a (13%) and the E-isomer 16b
(50%). Dealkylation of isomeric mixture 22d123d with
Me3SiI in CHCl3 gave, after chromatography on Dowex 1
(formate), the E,Z-iodophosphonate 26b (32%) followed by
the target phosphonates 15b116b (25%). It is clear that an
increased acidity (HI.HBr) and nucleophilicity/
I(2).Br(2)/facilitates the formation of side-product 26b
over that of 26a as observed for the reactivity of alkenes
toward hydrogen halides.27
The cytosine phosphonates 15c116c were obtained as
follows. The reaction of N4-acetylcytosine with diethyl phos-
phonate 21a (K2CO3 in DMF at 1008C, work-up with metha-
nol) afforded a 1.2:1 mixture of Z- and E-isomers 22e123e
(70%) that were inseparable by chromatography. A similar
reaction with diisopropyl phosphonate furnished a 1:1
isomeric mixture 22f123f (60%). Dealkylation of 22e123e
with Me3SiBr and subsequent chromatography on Dowex 1
afforded cyclic phosphonate 27a (10%) followed by a mixture
of the Z/E-isomers 15c116c (40%) in the ratio of 2.4:1.
Alkylation±elimination of 2-amino-6-chloropurine with
diisopropyl phosphonate 21b was perfomed with K2CO3
in DMF at 1108C to give the Z and E- isomers 22c123c
(56%). In this case, chromatographic separation on a silica
gel column was successful to afford ®rst the Z-isomer 22c
(24%) followed by E-isomer 23c (31%). This elution pattern
followed the trend observed previously for the Z- and E-
isomers of methylenecyclopropane analogues1 1 and 2
(Bˆ2-amino-6-chloropurine). Hydrolysis of 22c and 23c
The structure of 27a isomeric with 16c was con®rmed by

6050
H.-P. Guan et al. / Tetrahedron 58 (2002) 6047±6059
Compound 25 is then a hydrolysis product of 27b. It is
also possible that a preferential formation of cyclic phos-
phonate 27a from the E-isomer 16c via 26c can explain a
shift in the Z/E isomeric ratio in favor of the Z-isomer 15c
(see 15c116c).
B. Full-length phosphonates. Compounds 17 and 18 are
homologues of foreshortened phosphonates 15 and 16.
Initially, the displacement of mesyloxy group of methane-
sulfonate 19 (Scheme 1) with a lithium salt of diisopropyl
methylphosphonate was considered as the shortest route to a
key intermediate 31. However, attempts at such an alkyl-
ation were fruitless. Therefore, a more circuitous route was
adopted (Scheme 3). The sequence started with the ethyl
2-bromo-2-methylcyclopropane carboxylate23 (32) which
was reduced to 2-bromo-2-methylcyclopropanemethanol
(33) with DIBALH in hexane±ether mixture in 88% yield.
The latter was converted to dibromo derivative 34 using
Ph3P-NBS reagent30 in CH2Cl2 (95%). Reaction with a
lithium salt of diisopropyl methylphosphonate was smooth
to give the bromo phosphonate intermediate 35 (86%).
Elimination of the elements of HBr using NaH and a cata-
lytic amount of ethanol31 furnished methylenecyclopropane
phosphonate 31 (64%). Addition of bromine effected by
pyridinium tribromide gave the E,Z-dibromo phosphonate
36 in 91% yield. Alkylation±elimination procedure with
adenine using K2CO3 in DMF at 1108C gave the Z,E-
isomeric mixture of 37a138a (67%) which was not separ-
able by chromatography. Dealkylation with Me3SiBr in
DMF furnished target phosphonates 17a and 18a which
were separated in a manner similar to the lower homologues
15a and 16a by ion exchange chromatography on Dowex 1
(formate) in 41 and 36% yield, respectively. As in the case
of foreshortened analogues 15a and 16a, the Z-isomer 17a
was eluted prior to the E-isomer 18a.
Scheme 2.
UV, NMR and mass spectra. A large down®eld shift of the
31P resonance (44.7 ppm) relative to acyclic phosphonates
15c and 16c (24 ppm) is characteristic for ®ve-membered
ring cyclic phosphonates28 (48 ppm). It is likely that phos-
phonate 25 is a hydrolysis product of a similar intermediate
27b which was not isolated. It is also possible that
compounds 27a and 27b are generated from halogeno
derivatives 26c and 26d (Scheme 2) although both inter-
mediates have not been observed in contrast to guanine
counterparts 26a and 26b. Ionization of 26c or 26d leads
to carbocation 28 which then undergoes a 1,2-hydride shift29
to give a resonance-stabilized ion 29 $ 30: This stabiliza-
tion can be expected stronger with more basic nucleosides
(cytosine, adenine) than less basic guanine. An intra-
molecular attack of the cyclopropane ring by a phosphonate
anion then gives the cyclic phosphonate 27a or 27b.
Alkylation±elimination of 2-amino-6-chloropurine with
dibromide 36 was performed using Cs2CO3 in DMF32
Scheme 3.

H.-P. Guan et al. / Tetrahedron 58 (2002) 6047±6059
6051
Table 1. Comparison of the relevant 13C NMR chemical shifts of isomeric
phosphonates and parent analogues
compounds 25, 26a, 26b and 27a in Scheme 1), no side-
products were isolated.
0
C3 (ppm)
0
C4 (ppm)
0
Dppm C3 ,4
0
Isomer
Comparison of the UV spectra of all target phosphonates
with the corresponding parent analogues1,2 established
that adenine and guanine phosphonates are 9-substituted
purines whereas the cytosine derivatives are 1-substituted
cytosines. It is also noteworthy that electrophoretic
mobility of full-length analogues 17a, 17b was signi®-
cantly slower than those of foreshortened phosphonates 15a,
16a.
Z-1a (BˆAde)a
Z-15a
Z-17a
6.7
9.9
8.1
9.7
11.5
10.3
6.6
9.6
8.1
19.7
13.4
18.5
18.1
11.5
16.8
19.6
12.8
18.3
17.9
11.4
16.2
13
3.5
10.4
8.4
0
E-2a (BˆAde)a
E-16a
E-18a
6.5
13
Z-1a (BˆGua)a
Z-15b
Z-17b
3.2
10.2
8.3
0.2
5.6
E-1a (BˆGua)a
9.6
11.2
10.6
NMR spectra. The isomeric structures of target phos-
phonates were con®rmed by NMR spectroscopy. Although
spectra of phosphonates and parent analogues were deter-
mined in different solvents (D2O vs DMSO-d6) some
comparisons relevant for isomeric assignment are possible.
E-16b
E-18b
Sodium salt, D2O.
DMSO-d6. The C3 and C4 values are from Ref. 1.
a
0
0
0
In a foreshortened series 15a, 15b, 16a and 16b the H5
0
00
which made possible to lower the temperature and shorten
the reaction time (708C for 5 h). Chromatography on a silica
gel column afforded individual isomers 37b and 38b in 24
and 25% yield, respectively. As in case of foreshortened
analogues 22c and 23c, the Z-isomer 37b was eluted before
the E-isomer 38b. Compounds 37b and 38b were hydro-
lyzed with formic acid to give guanine phosphonates 37c
and 38c in quantitative yields. Dealkylation of the Z-isomer
37c with Me3SiBr in DMF furnished the target phosphonate
17b (65%). In a similar fashion, the E-isomer 38c afforded
phosphonate 18b (67%).
protons are non-equivalent. The Dd5 ,5 of the Z-isomers
15a and 15b were 1.13 and 1.03, respectively. In contrast,
the E-isomers 16a and 16b exhibited signi®cantly lower
values, 0.46 and 0.25. A similar trend was observed for
0
the H5 resonances of Z- and E-isomers of parent analogues
1a and 2a (Bˆadenine or guanine).1 In the 13C NMR spec-
0
tra, the C3 resonances of the Z-isomers are located at a
higher ®eld from those of the E-isomers (Table 1) in both
series of analogues. The corresponding chemical shifts of
the full-lengths analogues 17a, 17b, 18a and 18b resemble
more closely the respective parent analogues than the fore-
shortened series 15a, 15b, 16a and 16b. This trend is also
The alkylation±elimination of N4-acetylcytosine with
dibromide 36 (K2CO3 in DMF at 1008C) gave an isomeric
mixture of phosphonates 37d138d in 68% yield inseparable
by chromatography. Work-up with methanol led to a
removal of the N4-acetyl group. Dealkylation with Me3SiBr
in DMF furnished phosphonates 16c117c (79%) which
were also not resolved by chromatography on Dowex 1
(formate). In contrast to foreshortened analogues (see
0
re¯ected in the Dppm values of C3 ,4
0
.
The NOE experiments with adenine phosphonates 15a and
16a were in line with these conclusions (Table 2). It was not
possible to get reliable data for both isomers at 258C,
probably due to molecular association of the E-isomer 16a
in solution but no dif®culty was observed at 508C. In the
Z-isomer 15a, NOE enhancements were observed between
Table 2. NOE data of sodium salts of (Z)- and (E)-phosphonates 15a and 16a at 508C
0
0
H8´´´H1
H8´´´H4 1H5
1.2
5.9
0.5
0.5
0.6
1.3
8.2
1.6
2.8
4.1
4.1
8.3
3.4
H8´´´H1
H8´´´H3
H8´´´H3
0.6
1.0
1.0
1.2
0.4
1.0
2.5
3.3
3.4
1.0
0
0
00
0
0
H1 ´´´H8
0
H1 ´´´H3
0
H1 ´´´H3
0
H3 ´´´H1
0
H3 ´´´H4
00
H3 ´´´H1
00
H3 ´´´H5
0
H4 ´´´H8
0
0
H1 ´´´H8
0
H1 ´´´H4
0
H4 ´´´H1
0
H4 ´´´H3
00
H3 ´´´H8
0
H3 ´´´H8
0
H5 ´´´H1
00
0
0
0
0
0
0
00
0
0
H4 1H5 ´´´H8
0
H5 ´´´H3
00
H5 ´´´H3
0
00
0
0 00
H5 and H5 were assigned arbitrarily.

6052
H.-P. Guan et al. / Tetrahedron 58 (2002) 6047±6059
0
the purine H8 and proximate H4 1H5 (4.1±5.9%) but none
0
Section 4. Fractions (25 mL) were collected using a LKB
Ultrorac 7000 Fraction Collector using a UV detector
(254 nm) LKB Uvicord II (LKB Produkter, Bromma 1,
Sweden) and Recorder Model 201 (Ross Recorders, Sparks,
Nevada). The ¯ow-rate was 5 mL/min. Maintaining a high
¯ow-rate is essential to prevent precipitation of phospho-
nates in the column. Paper electrophoresis was run on a ¯at-
bed instrument (Savant Instruments, Inc., Hicksville, New
York) and Whatman No. 1 paper for 2 h at 108C and
40 V/cm in 0.02 M Na2HPO4 (pH 7.0). The relative
mobilities refer to that of AMPˆ1.00.
0
with the more distant H3 or H3 . In contrast, the strongest
00
0
interaction of H8 of the E-isomer 16a was with H3 and H3
00
(NOE enhancements 1.0±3.4%). A similar pattern of NOE
was seen in the Z- and E-isomers of parent analogues 1 and 2
(Bˆadenine).1
It is also of interest to note that anisochronism of dia-
stereotopic methylene, methine and methyl groups was
observed in the 13C NMR spectra of some diethyl and diiso-
propyl phosphonates but the 31P resonances were in all cases
isochronous. Thus, methylenecyclopropane phosphonates
20a and 20b exhibited signals of non-equivalent CH2
(ethyl) and CH (isopropyl) groups (two overlapped C,P
doublets at 61.9, 61.8 and 70.2, 70.1 ppm, respectively).
The signals of methyl groups were isochronous. This
apparently re¯ects the diastereotopicity of alkoxy groups
4.1.1. Diethyl (methylenecyclopropyl)methylphospho-
nate (20a). Diethyl phosphite (4.1 mL, 32 mmol) was
added dropwise to a stirred suspension of NaH (50% in
mineral oil, 1.54 g, 32 mmol) in THF (50 mL) at 08C. The
mixture was then stirred at room temperature for 2 h where-
upon it was cooled to 2408C. A solution of (methylene±
0
in 20a and 20b attached to a prochiral phosphorus (the C4
is chiral). By contrast, diisopropyl phosphonate 31 (homo-
logue of 20b) exhibited only a single doublet for CH of
isopropyl at 70.0 ppm. Apparently, when an extra methyl-
cyclopropyl)methyl
methanesulfonate23
19
(2.5 g,
15.4 mmol) in THF (10 mL) was added dropwise with stir-
ring which was continued at room temperature for 24 h. The
reaction was quenched with water (10 mL) at 08C followed
by saturated aqueous NaHCO3 (100 mL) and the mixture
was extracted with EtOAc (3£50 mL). The combined
organic phase was washed successively with saturated
aqueous NaHCO3, NH4Cl, brine, and it was dried
(Na2SO4). The solvent was removed in vacuo and the resi-
due was chromatographed on a silica gel column in hexane/
EtOAcˆ3:1!2:1) to give product 20a (2.76 g, 88%) as a
colorless oil. 1H NMR (CDCl3) d 5.52 (1H, s) and 5.41 (1H,
s), 4.12 (4H, m), 1.81 (2H, m), 1.61 (1H, m), 1.33 (7H, m),
0.90 (1H, m). 13C NMR 134.5 (d), 104.6, 61.9 and 61.8 (2
overlapped d, Jˆ7.0 Hz), 29.6 (d, Jˆ141.0 Hz), 16.7 (d,
Jˆ5.0 Hz), 10.2 (d, Jˆ11.0 Hz), 9.0 (d, Jˆ5.6 Hz). 31P
NMR 27.3. EI-MS 204 (M, 2.9), 148 (100.0). HRMS
calcd for C9H17O3P 204.0915; found 204.0916.
0
ene group is interposed between the chiral (C4 ) and
prochiral (phosphorus) center, the diastereotopic effect is
no longer observable. Non-equivalency of ethoxy groups
1
in diethyl phosphorothioate was established by H and 31P
NMR spectra.33 Anisochronous 13C NMR signals, were
observed in compounds with geminal prochiral groups
such as diisopropyl alkylmalonates34 and 2-isopropylmalon-
dialdehyde tetraethyl acetal.35 Extra 13C resonances were
also found in diisopropyl phosphonates 37b and 38b.
Thus, the CH signal of iPr in Z-isomer 37b appeared as
two overlapped doublets at 70.4 ppm and similar splitting
was also observed for CH3 groups at 24.3 ppm. By contrast,
only the CH3 resonances of the E-isomer 38b were aniso-
chronous and no such splittings were seen in the lower
homologues 22c and 23c.
4.1.2. Diisopropyl (methylenecyclopropyl)methylphos-
phonate (20b). The procedure described above was
performed with diisopropyl phosphite (5.4 mL, 32 mmol)
and the reaction mixture was stirred at 458C for 24 h to
afford product 20b (3.1 g, 84%) as a colorless oil. 1H
NMR (CDCl3) d 5.51 (1H, s) and 5.38 (1H, s), 4.70 (2H,
m), 1.75 (2H, m), 1.60 (1H, m), 1.25 (12H, 2d1m), 0.89
(1H, m). 13C NMR 134.8 (Jˆ10.0 Hz), 104.4, 70.2 and 70.1
(2 overlapped d, Jˆ8.0 and 7.1 Hz), 30.8 (d, Jˆ142.0 Hz),
24.3 (d, Jˆ5.0 Hz), 10.2 (2 overlapped d, Jˆ10.0 Hz), 9.2
(Jˆ5.1 Hz). 31P NMR 27.0. EI-MS 233 (M1H, 0.8), 148
(100.0). HRMS calcd for C11H22O3P (M1H) 233.1306;
found 233.1312.
3. Biological activity
All target phosphonates were found inactive against herpes-
viruses (HSV-1, HSV-2, HCMV, VZV and EBV) as well as
against hepatitis B virus (HBV) and HIV-1. Guanine phos-
phonate 15b which inhibited VZV in HFF culture with
EC50/CC50 (mM) 2.3/.317 (cytopathic effect inhibition
assay) and 24/.317 (plaque reduction assay) was an
exception.
4. Experimental
4.1.3. Diethyl (E,Z)-(2-bromomethyl-2-bromocyclo-
propyl)methylphosphonate (21a). Pyridinium hydro-
bromide perbromide (5.1 g, 16 mmol) was added in
4.1. General methods
See Ref. 1 The UV spectra were determined in ethanol or
0.01 M Na2HPO4 (pH 7). The 1H, 13C and 31P NMR spectra
were determined with the 300, 400 or 500 MHz instruments.
For less volatile compounds the FAB-MS (thioglycerol
matrix unless stated otherwise) and electrospray ionization
spectra (ESI-MS, direct injection, H2O/MeOH and NaCl or
KCl) were used unless stated otherwise. Anion exchange
chromatography was performed on Dowex 1X2-200
columns, 25£2.5 cm in a formate form using linear
gradients of formic acid at concentrations speci®ed in
portions to
a solution of compound 20a (2.76 g,
13.5 mmol) in CH2Cl2 (100 mL) at 08C. The mixture was
stirred at room temperature for 3 h whereupon an additional
portion of CH2Cl2 (100 mL) was added. The organic phase
was washed successively with aqueous NaHSO3, 1 M HCl,
NaHCO3 and brine and it was dried over Na2SO4. The
solvent was evaporated in vacuo and the crude product
was chromatographed on a silica gel column using hexane±
EtOAcˆ4:1!3:1!2:1) to give compound 21a (4.7 g, 96%)

H.-P. Guan et al. / Tetrahedron 58 (2002) 6047±6059
6053
1
as a colorless oil. H NMR (CDCl3) d 4.10 (4H, m), 3.82
7.37 (1H, 2s, 1:1), 7.45 and 7.44 (2H, 2s), 4.59 (2H, m), 2.34
(0.5H, dt, Jˆ16.2 and 4.4 Hz), 2.02 (1H, m), 1.80 and 1.74
(1.5H, m), 1.57 (1H, m), 1.42 (0.5H, m), 1.15±1.14 (12.5H,
m). 13C NMR d 156.7, 153.8, 153.7, 148.9, 148.8, 138.7,
137.7, 119.1, 116.56, 116.5, 112.0, 111.4, 70.2, 70.0, (2d,
Jˆ6.7 Hz), 30.1, 29.0 (2d, Jˆ140.3 Hz), 24.5 (d,
Jˆ4.4 Hz), 24.4 (d, Jˆ3.0 Hz), 24.3 (d, Jˆ6.7 Hz), 11.9
(d, Jˆ12.7), 11.7 (d, Jˆ4.4 Hz), 9.6 (d, Jˆ6.0 Hz), 9.5 (d,
Jˆ5.2 Hz). 31P NMR 28.2, 28.1. EI-MS 365 (M, 4.0), 200
(100.0). HRMS calcd for C16H24N5O3P 365.1617; found
365.1616.
(dd), 3.68 (d) and 3.57 (dd, JABˆ12.7 Hz, total 2H), 2.30
(1H, m), 1.82 (1H, m), 1.61 (1H, m), 1.50 (1H, m), 1.35
(6H, m), 0.90 (1H, m). 13C NMR 62.2 (2 poorly resolved
d, Jˆ4.5 Hz), 44.5, 41.3, 35.4 (Jˆ15.7 Hz), 25.3 (d,
Jˆ141.8 Hz), 25.2 (d, Jˆ5.1 Hz), 25.1 (d, Jˆ4.5 Hz), 16.7
(Jˆ5.2 Hz). EI-MS 285, 283 (M2Br, 61.7, 63.8), 147
(100.0). HRMS calcd for C9H1779BrO3P (M2Br)
283.0099; found 283.0095. Anal. Calcd for C9H17Br2O3P:
C, 29.70; H, 4.71; P, 8.51; Br, 43.91. Found: C, 29.65; H,
4.89; P, 8.66; Br, 43.79.
4.1.4. Diisopropyl (E,Z)-(2-bromomethyl-2-bromocyclo-
propyl)methyl phosphonate (21b). The procedure
described above for compound 21a was used with phospho-
nate 20b (3.1 g, 13.3 mmol). Product 21b was obtained as a
4.1.7. (Z)-, (E)-9-{[2-(Phosphonomethyl)cyclopropyl-
idene]methyl}adenine (15a, 16a) and (E)-9-(4-phos-
phono-3-hydroxymethyl-1-buten-1-yl)adenine
(25).
Me3SiI (3.58 mL, 25.1 mmol) was added dropwise with stir-
ring to a solution of isomers 22a123a (2.12 g, 6.3 mmol) in
CHCl3 (50 mL) at 2408C under N2. The mixture was then
allowed to warm to room temperature and the stirring was
continued for 6 h. The solvent was evaporated, the resultant
yellow syrup was dried at 5 torr and room temperature over-
night. It was dissolved in water and the solution was lyo-
philized. The crude product was redissolved in water and the
pH was adjusted to 8 with NH4OH. The solution was put on
the top of a Dowex-1 column (see Section 4.1), the column
was washed with water till the disappearance of UV absorp-
tion and the products were eluted with a linear gradient of
formic acid (0.06!0.08 and 0.08!0.12 M, 1 L each). The
Z-isomer 15a was eluted ®rst followed by E-isomer 16a and
compound 25. Fractions containing the products were
pooled and evaporated to approximately 1/10 of the original
volume. The precipitated white solids were ®ltered off to
give the Z-isomer 15a (297 mg, 17%), E-isomer 15a
(420 mg, 24%) and compound 25 (88 mg, 5%).
1
colorless oil (5.1 g, 100%) in .90% purity (1H NMR). H
NMR (CDCl3) d 4.62 (m, 2H), 3.72 (d), 3.62 (s) and 3.52 (d,
JABˆ12 Hz, 2H), 2.13 (m, 1H), 1.80 (m, 1H), 1.50 (m, 1H),
1.37 (m, 1H), 1.12 and 1.10 (2s, 12H, CH3), 0.86 (t,
Jˆ7.1 Hz, 1H). 13C NMR 70.72 and 70.65 (2 d, Jˆ3.0
and 4.0 Hz), 41.4, 35.6 (d, Jˆ16.1 Hz), 26.4 (d,
Jˆ144.1 Hz), 25.4 (d, Jˆ6.0 Hz), 25.2 (d, Jˆ5.1 Hz), 24.2
(Jˆ3.0 Hz). 31P NMR 26.5, 28.0. EI-MS 395, 393, 391 (M,
7.8, 15.7, 8.2), 313, 311 (M2Br, 16.2, 18.5), 147 (100.0).
HRMS calcd for C11H22O3P79Br2 390.9673; found
390.9677.
4.1.5. (E,Z)-9-{[2-(Diethylphosphonomethyl)cyclopro-
pylidene]methyl}adenine (22a123a).
A mixture of
compound 21a (1.46 g, 4 mmol), adenine (0.825 g,
5.2 mmol) and ¯ame-dried K2CO3 (2.76 g, 20 mmol) in
DMF (25 mL) was stirred at 1108C for 18 h. The solids
were ®ltered off and washed with DMF (2£8 mL). The
solvent was evaporated and the crude product was
chromatographed on
a
silica gel column (CH2Cl2/
Z-Isomer 15a: mp 237±2438C. UV max (pH 7) 261 nm (1
13,800), 228 (1 29,300). Electrophoretic mobility 0.80 of
AMP. 1H NMR (sodium salt, D2O) d 8.11 (1H, s, H8), 7.94
MeOHˆ30:1!20:1) to give a mixture of the E- and
Z-isomers 22a123a (0.77 g, 57%) as a white gum and
9-ethyladenine (24, 0.186 g, 28%) which was identical
with an authentic sample.24 UV max (EtOH) 262 nm (1
0
0
(1H, s, H2), 6.94 (1H, s, H1 ), 2.08 (1H, td, Jˆ16 Hz, H5 )
0
partly overlapped with 2.00 (1H, m, H4 ), 1.67 (1H, t,
1
0
00
14,500), 227 (1 31,000). H NMR (DMSO-d6) d 8.47 and
8.41 (1H, 2s, 1.5:1), 8.18 and 8.17 (1H, 2s), 7.54 and 7.39
(1H, 2s, 1.5:1), 7.34 (2H, s), 4.03 and 3.95 (4H, m), 2.37
Jˆ9.2 Hz, H3 ), 1.32 (1H, t, Jˆ6.4 Hz, H3 ), 0.96 (1H, dd,
Jˆ15.6 and 11 Hz, H5 ). 13C NMR 155.0 (C6), 152.3 (C2),
00
3
0
146.6 (C4), 138.9 (C8), 121.3 (d, Jˆ15.2 Hz, C2 ), 117.5
3
2
1
0
0
0
(0.4H, dt, Jˆ16.2 Hz and Jˆ4.8 Hz), 2.07 (1H, m), 1.84
(1.6H, m), 1.71 and 1.62 (1H, m), 1.44 and 1.31 (1H, m,
1.5:1), 1.28 (m) and 1.16 (6H, m, 1.5:1). 13C NMR d 156.7,
153.8, 153.7, 149.0, 138.8, 137.8, 119.1, 116.8, 112.0,
111.6, 61.9 (d, Jˆ5.9 Hz), 28.8 (d, Jˆ137.3 Hz), 27.8 (d,
Jˆ138.8 Hz), 17.0 (d, Jˆ3.0 Hz), 16.9 (d, Jˆ5.9 Hz), 12.0
(d, Jˆ12.7 Hz), 11.5, 9.6, 9.3. 31P NMR 30.2, 30.1. EI-MS
337 (M, 3.2), 200 (100.0). HRMS calcd for C14H20N5O3P
337.1304; found 337.1303. Anal. Calcd for C14H20N5O3P:
C, 49.85; H, 5.98; N, 20.76; P, 9.18. Found: C, 50.08; H,
5.94; N, 20.85; P, 9.31.
(C5), 108.6 (C1 ), 31.3 (d, Jˆ129.0 Hz, C5 ), 13.4 (C4 ),
9.9 (C3 ). 31P NMR 20.7. FAB-MS 282 (M1H, 29.6), 91
0
(100.0). Anal. Calcd for C10H12N5O3P: C, 42.71; H, 4.30; N,
24.90; P, 11.01. Found: C, 42.74; H, 4.53; N, 24.60; P,
10.87.
E-isomer 16a: mp 276±2878C. UV max (pH 7) 261 nm (1
14,600), 223 (1 28,100). Electrophoretic mobility 0.79 of
AMP. 1H NMR (sodium salt, D2O) d 8.00 (1H, s, H8), 7.76
0
(1H, s, H2), 6.96 (1H, s, H1 ), 1.86 (1H, m, H4 ), 1.73 (1H, td,
0
0
0
Jˆ5.6 and Jˆ15 Hz, H5 ), 1.61 (1H, t, Jˆ8.8 Hz, H3 ), 1.27
00
(1H, dt, Jˆ8.0 and 15.2 Hz, H5 ) partly overlapped with
1.21 (1H, m, H3 ). 13C NMR 154.6 (C6), 152.0 (C2), 146.2
00
4.1.6. (E,Z)-9-{[2-(Diisopropylphosphonomethyl)cyclo-
propylidene]methyl}adenine (22b123b). A mixture of
compound 21b (1.96 g, 5 mmol), adenine (0.88 g,
6.5 mmol) and K2CO3 (3.45 g, 25 mmol) in DMF (30 mL)
was treated as described above for isomers 22a123a to give
product 22b123b as a foam (1.26 g, 69%). UV max (EtOH)
3
0
(C4), 137.9 (C8), 121.1 (d, Jˆ12.1 Hz, C2 ), 117.1 (C5),
108.9 (C1 ), 32.4 (d, Jˆ128.9 Hz, C5 ), 11.5 (C3 , C4 ). 31P
NMR 21.0. FAB-MS 282 (M1H, 10.0), 91 (100.0). Anal.
Calcd for C10H12N5O3P: C, 42.71; H, 4.30; N, 24.90; P,
11.01. Found: C, 42.60; H, 4.46; N, 24.80; P, 10.87.
1
0
0
0
0
1
262 nm (1 14,300), 227 (1 29,800). H NMR (DMSO-d6)
8.46 and 8.40 (1H, 2s, 1:1), 8.20 and 8.18 (2H, 2s), 7.57 and
Compound 25: mp 235±2388C. UV max (pH 7) 260 nm (1

6054
H.-P. Guan et al. / Tetrahedron 58 (2002) 6047±6059
14,800), 223 (1 27,800). 1H NMR (sodium salt, D2O) d 8.12
(1H, s), 7.98 (1H, s), 6.85 (1H, d, Jˆ14.8 Hz), 6.17 (1H, dd,
Jˆ8.8 and 14.0 Hz), 3.76 (1H, dd, Jˆ5.6 and 11.2 Hz), 3.57
(1H, d, Jˆ6.4 and 11.2 Hz), 2.75 (1H, m), 1.56 (2H, dd,
Jˆ6.4 and 16.8 Hz). 13C NMR 155.3, 152.6, 147.6, 139.9,
lyophilized to give the Z-isomer 22d (0.86 g, 98%) as a
white solid. In a similar fashion, E-isomer 23d (1.14 g,
100%) was obtained from compound 23c (1.21 g, 3.0 mmol).
Z-isomer 22d: mp 215±2208C. UV max (EtOH) 270 nm (1
11,300), 227 (1 28,400). 1H NMR (DMSO-d6) d 11.85 (1H,
s), 8.70 (1H, s), 7.11 (1H, s), 6.56 (2H, brs), 4.75 (2H, m),
2.17 (1H, m), 2.11 (1H, m), 1.67 (1H, m), 1.60 (1H, m), 1.24
(13H, m). 13C NMR 156.1, 154.4, 150.5, 134.7, 121.7,
111.4, 110.7, 70.8, 30.7 (d, 1Jˆ143.5 Hz), 24.6, 12.01,
10.5. 31P NMR 28.0. ESI-MS (3-nitrobenzyl alcohol1NaCl/
KCl) 801 (2M1K, 10.1), 785 (2M1Na, 9.2), 763 (2M1H,
74.6), 420 (M1K, 7.7), 404 (8.9), 382 (M1H, 100.0).
3
3
127.4 (d, Jˆ12.1 Hz), 120.0, 118.2, 66.0 (d, Jˆ8.0 Hz),
39.1, 31.9 (d, 1Jˆ128.0 Hz). 31P NMR 20.5. ESI-MS
(MeOH1NH4OH) 300 (M1H, 100.0). Anal. Calcd for
C10H14N5O4P´H2O: C, 37.86; H, 5.08; N, 22.08; P, 9.76.
Found: C, 38.26; H, 5.29; N, 21.59; P, 10.09.
In a similar fashion, the E1Z-isomers 22b123b (1.2 g,
3.39 mmol) and Me3SiI (1.88 mL, 13.1 mmol) in CHCl3
gave 15a (184 mg, 20%), 16a (203 mg, 22%) and 25
(55 mg, 4%).
E-isomer 23d: mp 185±1888C. UV max (EtOH) 269 nm (1
12,000), 229 (1 24,800). 1H NMR (DMSO-d6) d 11.68 (1H,
s), 8.82 (1H, s), 7.34 (1H, s), 6.56 (2H, brs), 4.77 (2H, m),
2.02 (2H, m), 1.77 (1H, m), 1.64 (1H, m), 1.31 (13H, m). 13C
NMR 155.9, 154.4, 150.3, 134.3, 122.8, 111.9, 110.6, 70.0,
4.1.8. (Z)- and (E)-2-Amino-6-chloro-9-{[2-(diisopropyl-
phosphonomethyl)cyclopropylidene]methyl}purine (22c)
and (23c). A mixture of compound 21b (3.92 g, 10 mmol),
2-amino-6-chloropurine (2.03 g, 12 mmol) and K2CO3
(6.9 g, 50 mmol) in DMF (80 mL) was stirred at 1108C for
18 h. The solids were ®ltered off and washed with DMF
(2£20 mL). The solvent was evaporated and the crude
product was chromatographed on a silica gel column
(CH2Cl2/MeOHˆ30:1) to give a mixture of isomers
22c123c (2.25 g, 56%) which were resolved by repeated (3
times) chromatography. Solvent EtOAc/MeOHˆ40:1!30:1
eluted the faster moving Z-isomer 22c (0.96 g, 24%) and
CH2Cl2/MeOHˆ30:1 afforded the slower E-isomer 23c
(1.24 g, 31%).
1
30.56 (d, Jˆ143.0 Hz), 24.4, 11.8, 9.46. 31P NMR 29.7.
FAB-MS (3-nitrobenzyl alcohol1KCl) 420 (M1K, 88.3),
382 (M1H, 100.0).
4.1.10. (Z)-, (E)-9-{[2-(Phosphonomethyl)cyclopropyl-
idene]methyl}guanine (15b), (16b) and 9-{[1-Bromo-2-
(phosphonomethyl)cyclopropyl]methyl}guanine (26a).
Me3SiBr (1.5 mL, 11.0 mmol) was added dropwise with
stirring to
a solution of compound 22d (840 mg,
2.2 mmol) in DMF (50 mL) at 2408C. The mixture was
then allowed to warm to room temperature and stirred for
10 h. The work-up and chromatography followed the pro-
cedure described for compounds 15a, 16a and 25 using a
linear gradient of formic acid (0.08!0.18 M and
0.18!0.28 M, 1 L each). Compound 26a (85 mg, 10%)
was eluted ®rst followed by the Z-isomer 15b (380 mg,
58%). Compound 26a (122 mg, 13%) and the E-isomer
16b (369 mg, 50%) were obtained from intermediate 23d
(952 mg, 2.5 mmol) following a similar procedure.
Z-isomer 22c: mp 172±1748C. UV max (EtOH) 311 nm (1
7500), 233 (1 27,900). H NMR (CDCl3) d 7.99 (1H, s),
1
7.17 (1H, s), 5.78 (2H, brs), 4.67 (2H, m), 2.23 (1H, ddd,
Jˆ4.0, 15.2 and 18.6 Hz), 2.06 (1H, m), 1.62 (1H, td,
2
3Jˆ9.0 Hz, Jˆ1.6 Hz), 1.49 (1H, ddd, Jˆ9.4, 15.4 and
18.2 Hz), 1.23 (13H, m). 13C NMR 159.9, 152.5, 151.5,
139.9, 125.0, 117.0 (d, 3Jˆ14.9 Hz), 111.2, 70.8 (d,
1
3
2Jˆ6.7 Hz), 30.1 (d, Jˆ142.5 Hz), 24.3 (d, Jˆ3.7 Hz),
11.9 (d, Jˆ4.5 Hz), 10.4 (d, Jˆ4.5 Hz). 31P NMR 27.5.
EI-MS 399, 401 (M, 8.3, 2.8), 234 (100.0). HRMS calcd for
C16H23ClN5O3P 399.1227; found 399.1224. Anal. Calcd for
C16H2335ClN5O3P: C, 48.07; H, 5.80; N, 17.52, P, 7.75.
Found: C, 48.28; H, 5.81; N, 17.31; P, 8.14.
Z-isomer 15b: mp.3508C (decomp.). UV max (pH 7)
265 nm (1 13,400), 229 (1 32,900). Electrophoretic
mobility 1.11 of AMP. H NMR (sodium salt, D2O) d
2
3
1
7.75 (1H, s), 6.71 (1H, s), 2.05 (1H, t, Jˆ15.4 Hz), 1.86
(1H, m), 1.53 (1H, t, Jˆ9 Hz), 1.18 (1H, m), 0.97 (1H, td,
Jˆ15.6 and 11.2 Hz). 13C NMR 158.5, 153.5, 149.4, 136.6,
115.3, 120.2 (d, 3Jˆ15.1 Hz), 109.0, 30.8 (d, 1Jˆ130.0 Hz),
12.8, 9.6. 31P NMR 22.0. ESI-MS (H2O/MeOH) 595
(2M1H, 27.8), 298 (M1H, 100.0). Anal. Calcd for
C10H12N5O4P´H2O: C, 38.10; H, 4.48; N, 22.22; P, 9.83.
Found: C, 37.86; H, 4.59; N, 22.64; P, 9.70.
E-isomer 23c (isomeric purity 85%): mp 157±1608C. UV
max (EtOH) 310 nm (1 7300), 225 (1 25,400). H NMR
1
(CDCl3) d 8.06 (1H, s), 7.46 (1H, s), 6.45 (2H, brs), 4.75
(2H, m), 2.04 (1H, m), 1.87 (1, m), 1.74 (1H, dt, Jˆ9.0 Hz),
1.56 (1H, ddd, Jˆ8.4, 14.6 and 18 Hz), 1.31 (13H, m). 13C
NMR 160.2, 152.5, 151.4, 138.5, 124.6, 115.8 (d, 3Jˆ
8.1 Hz), 112.2, 70.7, 30.58 (d, 1Jˆ144.1 Hz), 24.3 (d,
3Jˆ4.0 Hz), 11.7 (d), 9.3 (d, 3Jˆ6.7 Hz). 31P NMR 27.6.
EI-MS 399, 401 (M, 7.6, 3.5), 234 (100.0). HRMS calcd for
C16H2335ClN5O3P 399.1227; found 399.1220. Anal. Calcd
for C16H23ClN5O3P: C, 48.07; H, 5.80; N, 17.52, P, 7.75.
Found: C, 48.21; H, 5.72; N, 17.54; P, 8.07.
E-isomer 16b: mp.3508C (decomp.). UV max (pH 7)
266 nm (1 11,800), 223 (1 30,600). Electrophoretic
mobility 1.08 of AMP. H NMR (sodium salt, D2O) d
1
7.86 (1H, s), 7.05 (1H, m, 1.86 (1H, m), 1.62 (2H, m),
1.37 (1H, td, Jˆ7.2 and 15.2 Hz), 1.20 (1H, m). 13C NMR
3
168.3, 161.3, 150.2, 135.4, 117.1, 120.8 (d, Jˆ11.1 Hz),
1
2
110.0, 32.6 (d, Jˆ129.0 Hz), 11.4 (d, Jˆ4.0 Hz), 11.2
3
4.1.9. (Z)- and (E)-9-{[2-(Diisopropylphosphonomethyl)-
cyclopropylidene]methyl}guanine (22d) and (23d). A
solution of compound 22c (0.92 g, 2.3 mmol) in formic
acid (80%, 20 mL) was heated at 908C for 6 h whereupon
it was evaporated. An aqueous solution of the residue was
(d, Jˆ8.1 Hz). 31P NMR 21.1. ESI-MS (MeOH1NaCl)
298 (M1H, 100.0), 320 (M1Na, 37.7), 595 (2M1Na, 5.7),
617 (2M1Na, 20.7). Anal. Calcd for C10H12N5O4P´0.8H2O:
C, 38.54; H, 4.40; N, 22.47; P, 9.94. Found: C, 38.66; H,
4.67; N, 22.43; P, 10.12.

H.-P. Guan et al. / Tetrahedron 58 (2002) 6047±6059
6055
Compound 26a (E,Z-isomers): mp 280±2908C. UV max
(pH 7) 253 nm (1 14,100), 200 (1 21,400). 1H NMR
(sodium salt, D2O) d 7.90 and 7.85 (1H, 2s), 4.47 and
4.20 (2H, JABˆ15.2 Hz), 2.04 (1H, td, Jˆ2.4 and
16.8 Hz), 1.85 (1H, m), 1.43 (1H, m), 1.20 (1H, m). 13C
NMR 159.4, 154.0, 152.1, 140.2, 115.8, 49.8, 36.5, 28.8
The isomeric mixture of 22f123f was obtained as a white
gum (1.59 g, 60%). UV max (EtOH) 296 nm (1 13,000),
231 (1 12,300), 206 (1 20,500). H NMR (CDCl3) d 8.19
1
(bs) and 8.03 (1H, bs) and 7.75 (1H, bs, 1:1), 7.60 (d,
Jˆ7.2 Hz), 7.43 (d) and 7.25 (d, total 2H), 6.02 (1H, d,
Jˆ7.6 Hz), 4.49 (2H, m), 1.98 (t, Jˆ14.6 Hz), 1.76 (m),
1.64 (m), 1.59 (m), 1.48 (m), 1.32 (m), 1.08 (m) and 0.99
(m, total 17H). 13C NMR 164.5, 154.3, 141.6, 140.7, 117.6,
116.6, 112.5, 112.4, 95.9, 95.7, 70.7, 70.5, 30.4 (d,
1Jˆ143.1 Hz), 29.8 (d, 1Jˆ142.5 Hz), 24.3, 11.3, 10.9,
9.0, 8.2). 31P NMR 27.9, 27.3. EI-MS 341 (M, 3.6), 43
(100.0). HRMS calcd for C15H24N3O4P: 341.1504; found
341.1501.
1
(d, Jˆ127.9 Hz), 24.9, 22.7. 31P NMR 20.9, 19.9. ESI-
MS (H2O/MeOH1NaCl/KCl) 418 and 416 (M1K, 36.0
and 31.1), 402 and 400 (M1Na, 25.6 and 26.2), 380 and
378 (M1H, 99.4 and 100.0).
4.1.11. (Z)-, (E)-9-{[2-(Phosphonomethyl)cyclopropyl-
idene]methyl}guanine (15b), (16b) and (E,Z)-9-{[1-iodo-
2-(phosphonomethyl)cyclopropyl]methyl}guanine (26b).
The procedure described above was followed using Me3SiI
(0.33 mL, 2.5 mmol) and isomeric mixture 22d123d
(190 mg, 0.5 mmol) in CHCl3 (10 mL) at 2408C. The
crude product was puri®ed by chromatography on Dowex 1
column using formic acid (0.10!0.30 M, 1 L each) to give
compound 26b (68 mg, 32%) and a mixture of Z- and
E-isomers 15b116b (38 mg, 25%).
4.1.14. (E)-, (Z)-9-{[2-(Phosphonomethyl)cyclopropyl-
idene]methyl}cytosine (15c116c) and cyclic phospho-
nate 27a. Isomers 22e123e (1.56 g, 5 mmol) in DMF
(50 mL) were treated with Me3SiBr (3.4 mL, 25.0 mmol)
at 2408C as described for compounds 15b and 16b. The
crude product was puri®ed by chromatography on Dowex 1
using formic acid (0.0!0.08 and 0.08!0.18 M, 1 L each)
to give a mixture of E,Z-isomers 15c116c (512 mg, 40%)
and cyclic phosphonate 27a (135 mg, 11%).
Compound 26b (E,Z-isomers): mp 290±3008C. UV max
(pH 7) 253 nm (1 14,300), 200 (1 20,800). 1H NMR
(sodium salt, D2O) d 7.86 and 7.81 (1H, 2s), 4.41 and
4.10 (2H, d and m, JABˆ15.2 Hz), 2.02 (1H, td, Jˆ3.4 and
19.2 Hz), 1.83 (1H, m), 1.39 (1H, dd, Jˆ2.8 and 7.2 Hz),
1.27 (1H, ddd, Jˆ17.4, 14.2 and 10.4 Hz), 1.16 (1H, t,
Jˆ7.4 Hz). 13C NMR 160.2, 154.4, 152.4, 141.1, 116.5,
Isomers 15c116c. Mp 230±2358C. UV max (pH 7) 291 nm
(1 12,000), 228 (1 12,500), 201 (1 16,600). 1H NMR
(sodium salt, D2O) d 7.78 (1H, d) and 7.66 (1H, d, Jˆ
7.5 Hz, 2.4:1), 7.10 (d, Jˆ1.5 Hz) and 6.93 (1H, s, 2.4:1),
5.85 (d) and 5.79 (1H, d, Jˆ7.5 Hz, 1:2.4), 1.87 (dt), 1.77
(m), 1.61 (m), 1.57 (dd), 1.50 (m), 1.38 (m), 1.06 (m), 1.05
(m), 0.91 (m, total 5H). 13C NMR 166.0, 157.1, 157.0,
142.8, 142.5, 19.8, 119.7, 115.2, 114.8, 96.6, 96.2, 31.9
1
50.7, 36.9, 29.5 (d, Jˆ127.9 Hz), 25.3, 23.0. 31P NMR
23.1, 21.7. FAB-MS 425 (M, 0.3), 297 (M2HI, 3.4), 93
(100.0). Anal. Calcd for C10H13IN5O4P: C, 28.25; H, 3.08;
N, 16.47; P, 7.29. Found: C, 28.41; H, 3.25; N, 16.50; P,
7.01.
1
1
(d, Jˆ131.0 Hz), 31.2 (d, Jˆ130.0 Hz), 12.3, 10.6 (d,
Jˆ8.3 Hz), 9.6 (d, Jˆ3.8 Hz), 8.8. 31P NMR 24.3, 23.6.
ESI-MS (H2O/MeOH) 258 (M1H, 100.0). Anal. Calcd for
C9H12N3O4P: C, 42.01; H, 4.70; N, 16.34; P, 12.05. Found:
C, 42.13; H, 4.72; N, 16.16; P, 11.81.
4.1.12. (E,Z)-9-{[2-(Diethylphosphonomethyl)cyclopro-
pylidene]methyl}cytosine (22e123e). A stirred mixture
of compound 21a (2.67 g, 7.3 mmol), N4-acetylcytosine
(1.35 g, 8.8 mmol) and K2CO3 (5.0 g, 36 mmol) in DMF
(80 mL) was heated at 1108C for 16 h. Methanol (10 mL)
was added dropwise, heating was discontinued and the
mixture was stirred for 3 h. After cooling, the solution
was evaporated and the crude product was chromatographed
on a silica gel column (CH2Cl2/MeOHˆ15:1!10:1) to give
a mixture of Z- and E-isomers 22e123e as a white gum
(1.60 g, 70%). UV max (EtOH) 296 nm (1 12,800), 231
Compound 27a. UV max (pH 7) 291 nm (1 14,200), 228 (1
13,100), 201 (1 20,400). 1H NMR (sodium salt, D2O) d 7.63
(1H, d, Jˆ7.2 Hz), 6.84 (1H, d, Jˆ13.6 Hz), 5.92 (1H, dd,
Jˆ7.2 Hz), 5.71 (1H, dd, Jˆ8.0 and 13.6 Hz), 4.12 (1H,
ddd, Jˆ7.2, 8.8 and 16.0 Hz), 3.65 (1H, td, Jˆ9.6 and
4.8 Hz), 3.22 (1H, m), 1.93 (1H, m), 1.56 (1H, td, Jˆ10.4
and 14.4 Hz). 13C NMR 166.2, 148.3, 146.3, 125.5, 125.0,
95.5, 68.5, 38.5, 26.8 (d, 1Jˆ120.2 Hz). 31P NMR 44.7. ESI-
MS (H2O/MeOH) 258 (M1H, 100.0).
1
(1 12,300), 205 (1 19,600). H NMR (DMSO-d6) d 7.94
(d, Jˆ8.0 Hz) and 7.80 (1H, d, Jˆ7.2 Hz, 1:1.2), 7.47 (d),
7.45 (s) and 7.27 (d, total 3H), 5.83 (1H, 2 overlapped d),
3.94 (4H, m), 1.65 (2H, m), 1.22 (6H, m, 6H), 2.25 (dt), 1.99
(m), 1.42 (t), 1.13 (m), 0.83 (t, total 3H). 13C NMR 166.1,
154.7, 154.6, 141.6, 140.8, 117.0, 116.7, 112.5, 112.4, 96.0,
95.8, 61.7, (t, 2Jˆ6.7 Hz), 28.7 (d, 1Jˆ138.0 Hz), 28.0
Diisopropyl phosphonates 22f123f (716 mg, 2.1 mmol)
when treated with Me3SiBr (1.4 mL, 10.6 mmol) under
similar conditions gave phosphonates 15c116c (250 mg,
50%) and cyclic phosphonate 27a (78 mg, 16%).
1
3
(d, Jˆ137.3 Hz) 16.9, 11.1 (d, Jˆ12.7 Hz), 10.6, 8.2 (d,
3Jˆ5.9 Hz), 7.49. 31P NMR 30.4, 30.0. EI-MS 314 (M1H,
8.5), 43 (100.0). HRMS calcd for C13H20N3O4P: 313.1191;
found 313.1188.
4.1.15. Ethyl (E,Z)-2-bromo-2-methylcyclopropane
carboxylate (32). The described procedure23 was adapted
for a large-scale preparation as follows. Ethyl diazoacetate
(173.9 g, 1.65 mol) was added with the aid of a syringe
pump (20 mL/h) to a mixture of 2-bromo-1-propene
(260.1 g, 2.15 mol, Chemsampco, Gray Court, South
Carolina, distilled before use) and Rh2(OAc)4 (221 mg,
0.5 mmol) at room temperature with stirring (Dry Ice
condenser). The stirring was continued for 16 h, the
unreacted crude alkene was distilled off (bath temperature
4.1.13. (E,Z)-9-{[2-(Diisopropylphosphonomethyl)cyclo-
propylidene]methyl}cytosine (22f123f). The procedure
described above for 22e123e was followed using N4-acetyl-
cytosine (1.42 g, 9.26 mmol), compound 21b (2.79 g,
7.1 mmol), K2CO3 (4.91 g, 35.5 mmol) and DMF (80 mL).

6056
H.-P. Guan et al. / Tetrahedron 58 (2002) 6047±6059
608C, the receiver was cooled at 2788C, 135.4 g, 52%) and
the residue was distilled in vacuo to give ester 32 in two
fractions: bp 92±988C/28 torr, 137.22 g (40.2%, based on
ethyl diazoacetate, 65% Z(trans) isomer, bp 98±1168C/
32 mmol) in THF (50 mL). The mixture was stirred at room
temperature for 10 min and then it was cooled to 2788C.
Diisopropyl methylphosphonate (6.2 mL, 33 mmol) was
added and the resulting mixture was stirred at 2788C for
30 min. A solution of compound 34 (mixture of E/Z
isomers, 2.28 g, 10 mmol) in THF (10 mL) was then
added dropwise with stirring which was continued fo 6 h
at 2788C. The reaction was quenched with saturated NH4Cl
(50 mL) and the product was extracted with EtOAc
(3£50 mL). The combined organic phase was washed
successively with brine, aqueous NaHCO3, brine, and
dried (Na2SO4). The solvent was evaporated and the residue
was chromatographed on a silica gel column in hexane/
EtOAcˆ10:1!5:1!3:1) to give product 35 (2.8 g, 86%)
1
28 torr (80.82 g, 23.7, 90% E(cis)-isomer). The H NMR
data corresponded to those reported for the cis/trans
isomeric mixture.23
4.1.16. (Z)-2-Bromo-2-methylcyclopropanemethanol (33).
A 1 M solution of DIBALH in hexane (100 mL, 100 mmol)
was added dropwise into ethyl 2-bromo-2-methylcyclo-
propane carboxylate (32, 65% Z-isomer, 8.28 g, 40 mmol)
in Et2O (30 mL) at 08C with stirring under N2 over a period
of 30 min. The stirring was continued for another 2 h. The
reaction was quenched with water (5 mL) and 4 M HCl
(70 mL) was added to dissolve the gel formed. The mixture
was extracted with Et2O (3£30 mL). The combined organic
phase was washed successively with 1 M HCl, H2O, saturated
NaHCO3, H2O, brine and it was dried (Na2SO4). After
evaporation of the solvent, product 33 was obtained as a
colorless oil. Distillation in vacuo afforded 5.48 g (83%),
bp 102±1088C/28 torr, 77% Z-isomer. The 1H and 13C
NMR data corresponded to those reported23 for the 1R,2S
(Z)-isomer of 33.
1
as a colorless oil. H NMR (CDCl3) d 4.58 (2H, m), 1.79
(2H, m), 1.67 (5H, m1s), 1.16 (m1s), 0.81 (m), 0.62 (m),
0.34 (t, total 15H). 31P NMR 30.2, 29.8. EI-MS 328, 326 (M,
0.30, 0.23), 163 (100.0). HRMS calcd for C12H24O3P79Br
326.0646; found 326.0643.
4.1.19. Diisopropyl 2-(methylenecyclopropyl)ethyl-1-
phosphonate (31). NaH (1.76 g, 36.7 mmol) was added in
portions to a solution of compound 35 (3.0 g, 9.17 mmol) in
THF (60 mL) and DMF (20 mL). The stirred mixture was
heated in an oil bath (708C), EtOH (0.115 mL, 2 mmol) was
added and the heating was continued for 6 h. After cooling
to 08C the reaction was quenched by saturated aqueous
NH4Cl (100 mL). The product was extracted with EtOAc
(4£50 mL). The organic phase was washed with aqueous
NaHCO3 and brine, dried (Na2SO4) and it was evaporated.
Chromatography on a silica gel column in hexane/
EtOAcˆ10:1!5:1!3:1 gave product 31 (1.45 g, 64%) as
a colorless oil. 1H NMR (CDCl3) d 5.41 (1H, d), 5.34 (1H,
bs), 4.65 (2H, m), 1.83±1.74 (2H, m), 1.63 (2H, m), 1.48
(1H, m), 1.38 (12H, 2s), 1.24 (1H, m), 0.76 (1H, m). 13C
NMR 136.0, 103.3, 70.0 (2Jˆ5.9 Hz), 26.6 (d, 1Jˆ
117.1 Hz), 26.2 (d, 2Jˆ19.4 Hz), 24.3, 16.3 (d, 3Jˆ
20.1 Hz), 9.6. 31P NMR 30.7. ESI-MS (NaCl) 515 (2M1
Na, 100.0), 269 (M1Na, 19.5), 247 (M1H, 83.2).
4.1.17. (E,Z)-1-Bromo-1-methyl-2-bromomethylcyclo-
propane (34). NBS (9.91 g, 55.7 mmol) was added to a
solution of compound 33 (77% Z-isomer, 4.59 g,
27.8 mmol) in CH2Cl2 (14 mL). A solution of PPh3
(10.94 g, 41.7 mmol) in CH2Cl2 (14 mL) was then added
with stirring at such a rate that the temperature did not
exceed 408C. The resulting reddish solution was stirred at
room temperature for 1 h whereupon it was added dropwise
with stirring into pentane (300 mL). The precipitate was
®ltered off and the solvent was distilled off at an atmos-
pheric pressure to give a clear syrup which was stirred
again with pentane (30 mL). The solids were removed by
®ltration and the ®ltrate was evaporated to a colorless oil.
Distillation gave product 34 (79% Z-isomer, 6.04 g, 95%, bp
102±1068C/50 torr).
4.1.20. Diisopropyl E,Z-[2-(2-bromomethyl-2-bromo-
cyclopropyl)ethyl]-1-phosphonate
Another experiment performed with a 1:1 isomeric mixture
of compound 33 gave after distillation in vacuo using a
Vigreux column the Z-isomer of 34 (bp 85±908C/20 torr,
3.52 g, 44%) and E-isomer of 34 (bp 95±988C/20 torr,
4.0 g, 50%).
(36).
Pyridinium
hydrobromide perbromide (4.68 g, 14.6 mmol) was added
in portions with stirring to a solution of compound 31 (3.0 g,
12.2 mmol) in CH2Cl2 (100 mL) at 08C. The stirring was
continued for 3 h at room temperature. The reaction was
quenched with saturated aqueous NaHSO3 (100 mL) and
the water phase was extracted with CH2Cl2 (2£50 mL).
The combined organic phase was washed successively
with aqueous NaHSO3, 1 M HCl, NaHCO3, brine and then
it was dried over Na2SO4. Solvent was evaporated and the
crude product was chromatographed using hexane/
EtOAcˆ4:1!3:1!2:1) to give product 36 (4.5 g, 91%) as
an oil. The 31P NMR spectrum indicated 83% purity of the
E/Z-isomeric mixture of 36 which was used as such in the
next step. 1H NMR (CDCl3) d 4.64 (2H, m), 3.82, 3.57 (2d,
JABˆ11.2, 12 Hz), 3.73, 3.52 (JABˆ11.2 Hz, total 2H), 2.0±
1.6 (4H, 2m), 1.46 (1H, m), 1.30 (12H, 2s1m), 1.03 (t,
Jˆ6.8 Hz), 0.95 (m), 0.74 (t, Jˆ7.0 Hz, total 2H). 31P
NMR 29.8, 29.4. EI-MS 409, 407, 405 (1.39, 2.83, 1.57,
M1H), 327, 325 (6.93, 6.68, M2Br), 79 (100.0). HRMS
calcd for C12H2379BrO3P (M2Br) 325.0568; found
325.0568.
Z-isomer: 1H NMR (CDCl3) d 3.45 (1H, dd, Jˆ7.5
and 10.8 Hz), 3.30 (1H, dd, Jˆ9.0 and 10.5 Hz), 2.00
(1H, m), 1.81 (3H, s), 1.47 (1H, dd, Jˆ6.9 and 9.6 Hz),
0.71 (1H, t, Jˆ6.4 Hz). 13C NMR d 33.3, 32.4, 29.7, 25.2,
23.8. EI-MS 149 (66.9) and 147 (71.6, M2Br), 67 (100.0).
HRMS calcd for C5H879Br (M2Br) 146.9809; found
146.9808.
E-Isomer: 1H NMR (CDCl3) d 3.64 (1H, m), 3.47 (1H, m),
1.76 (3H, s), 1.17 (2H, m), 0.96 (1H, m). 13C NMR d 38.6,
36.5, 30.3, 27.7, 25.5. A mixture of both isomers was used in
a subsequent step.
4.1.18. Diisopropyl (E,Z)-2-[(2-bromo-2-methylcyclo-
propyl)ethyl]-1-phosphonate (35). HMPA (5.74 mL,
33 mmol) was added to a solution of BuLi (1.6 M, 20 mL,

H.-P. Guan et al. / Tetrahedron 58 (2002) 6047±6059
6057
4.1.21. (Z,E)-9-{[(2-Diisopropylphosphonoethyl)cyclo-
propylidene]methyl}adenine (37a138a). A mixture of
compound 36 (2.1 g, 5.1 mmol), adenine (905 mg,
6.7 mmol) and K2CO3 (3.6 g, 25.7 mmol) in DMF
(30 mL) was stirred at 1108C for 20 h. After cooling, the
solids were ®ltered off and washed with DMF (2£5 mL).
The solvent was evaporated in vacuo and the crude product
was chromatographed on a silica gel column (CH2Cl2/
MeOHˆ25:1!15:1) to give isomeric mixture 37a138a
(1.3 g, 67%) as a white gum. UV max (EtOH) 262 nm (1
14,200), 226 (1 29,900). 1H NMR (DMSO-d6) d 8.47, 8.35
(1H, 2s, 1:1), 8.17 (1H, s), 7.56, 7.36 (3H, 2s), 4.55, 4.47
(2H, 2m), 2.09 (m), 1.86 (m), 1.69 (m), 1.51 (m) and 1.35
(m, total 7H), 1.21, 1.16 (12H, 2d, Jˆ8.4 Hz). 31P NMR
30.3, 30.0. EI-MS 379 (M, 2.7), 378 (M2H, 11.0), 200
(100.0). HRMS calcd for C17H25N5O3P (M2H) 378.1695;
found 378.1693. Anal. Calcd for C17H26N5O3P: C, 53.82; H,
6.91; N, 18.46; P, 8.16. Found: C, 53.94; H, 6.83; N, 18.35;
P, 8.34.
give an isomeric mixture of 37b138b (3.8 g, 58%) which
was separated by repeated chromatography using EtOAc/
MeOHˆ40:1!30:1 for faster moving Z-isomer 37b and
then CH2Cl2/MeOHˆ30:1 for slower moving E-isomer
38b to give 37b (1.62 g, 24%, isomeric purity .95%) and
38b (1.66 g, 25%, 90% isomeric purity).
Z-isomer 37b: mp 154±1568C. UV max (EtOH) 311 nm (1
8900), 227 (1 30,100). H NMR (CDCl3) d 7.98 (1H, s),
1
7.18 (1H, s), 5.61 (2H, brs), 4.66 (2H, m), 2.19 (1H, m), 2.00
(1H, m), 1.78 (2H, m), 1.49 (2H, m), 1.23 (12H, d), 1.11
(1H, t, Jˆ7.0 Hz). 13C NMR 159.8, 152.6, 151.6, 139.8,
125.2, 118.9, 110.8, 70.4 (2 overlapped d, 2Jˆ5.9 Hz),
1
3
25.9 (d, Jˆ142.5 Hz), 25.4 (d, Jˆ4.4 Hz), 24.3 (2 over-
3
2
lapped d, Jˆ5.2 Hz), 18.3 (d, Jˆ18.6 Hz), 8.8. 31P NMR
30.3 ppm. EI-MS 415, 413 (M, 5.0, 7.4), 234 (100.0).
HRMS calcd for C17H2535ClN5O3P 413.1384; found
413.1385. ESI-MS (MeOH1NaCl) 849, 851 (2M1Na,
29.6, 35.9), 438, 436 (M1Na, 38.9, 100.0), 416, 414
(M1H, 10.8, 18.0). Anal. Calcd for C17H25ClN5O3P: C,
49.34; H, 6.09; Cl, 8.57; N, 16.92; P, 7.48. Found: C,
49.42; H, 6.17; Cl, 8.71; N, 16.82; P, 7.62.
4.1.22. (Z)- and (E)-9-{[2-(Phosphonoethyl)cyclopropyl-
idene]methyl}adenine (17a) and (18a). Me3SiBr (2.3 mL,
17 mmol) was added dropwise with stirring to a solution of
isomers 37a138a (1.27 g, 3.4 mmol) in DMF (40 mL) at
2408C. The mixture was then allowed to warm to room
temperature and the stirring was continued for 8 h. Solvents
were evaporated and the isomers 17a and 18a were
separated by chromatography on Dowex 1 as described
for phosphonates 15a and 16a. The Z-isomer 17a was eluted
®rst (397 mg, 41%) followed by the E-isomer 18a (362 mg,
36%).
E-Isomer 38b: mp 130±1338C. UV max (EtOH) 310 nm (1
9600), 230 (1 35,700). 1H NMR (CDCl3) 8.16 (1H, s), 7.35
(1H, s), 5.62 (2H, brs), 4.68 (2H, m), 1.83 (2H, m), 1.72 (2H,
m), 1.64 (1H, td), 1.25 (13H, m), 1.19 (1H, m). 13C NMR
159.7, 152.5, 151.5, 138.9, 125.0, 117.4, 110.6, 70.3 (d,
1
3
2Jˆ6.6 Hz), 26.8 (d, Jˆ142.6 Hz), 26.4 (d, Jˆ4.4 Hz),
2
2
24.3 (2 overlapped d, Jˆ7.5 and 3.8 Hz), 16.1 (d, Jˆ
19.4 Hz), 11.2. 31P NMR 29.9. ESI-MS (MeOH1NaCl)
851, 849 (2M1Na, 35.3, 46.1), 438, 436 (M1Na, 38.9,
100.0), 416, 414 (M1H, 15.0, 44.3). Anal. Calcd for
C17H25ClN5O3P´0.25H2O: C, 48.81; H, 6.14; Cl, 8.47; N,
16.74; P, 7.40. Found: C, 48.80; H, 6.15; Cl, 8.36; N,
16.84; P, 7.29.
Z-Isomer 17a: mp 261±2658C. UV max (pH 7) 260 nm (1
12,900), 224 (1 23,500). Electrophoretic mobility 0.60 of
AMP. 1H NMR (sodium salt, D2O) d 8.13 and 7.97 (2H, 2s),
6.96 (1H, s), 1.94 (2H, 2 overlapped m), 1.52±1.31 (4H, m),
1.15 (1H, t, Jˆ6.4 Hz). 13C NMR 155.0, 152.3, 146.6,
1
138.8, 121.4, 117.5, 108.8, 28.3 (d, Jˆ130.0 Hz), 26.7,
4.1.24. (Z)- and (E)-9-{[2-(Diisopropylphosphonoethyl)-
cyclopropylidene]methyl}guanine (37c) and (38c). A
solution of compound 37b (1.60 g, 3.87 mmol) in formic
acid (80%, 30 mL) was heated at 908C for 6 h whereupon
it was evaporated. The residue was lyophilized from water
to give the Z-isomer 37c (1.53 g, 100%) as a white gum. UV
18.5 (d, 2Jˆ21.1 Hz), 8.1. 31P NMR 22.6. ESI-MS
(MeOH) 296 (M1H, 100.0). Anal. Calcd for
C11H14N5O3P.H2O: C, 42.18; H, 5.15; N, 22.36; P, 9.89.
Found: C, 41.93; H, 5.08; N, 22.20; P, 10.26.
1
E-isomer 18a: mp 270±2738C. UV max (pH 7) 261 nm (1
14,100), 226 (1 30,200). Electrophoretic mobility 0.54 of
AMP. 1H NMR (sodium salt, D2O) d 8.19 and 7.95 (2H, 2s),
7.11 (1H, s), 1.84 (1H, m), 1.64±1.55 (5H, m), 1.20 (1H, m).
13C NMR 154.9, 152.2, 146.6, 138.2, 120.8, 117.3, 108.7,
max (EtOH) 271 nm (1 11,900), 228 (1 26,100). H NMR
(DMSO-d6) d 11.54 (1H, s), 8.75 (1H, s), 7.14 (3H, s), 4.44
(2H, m), 2.10 (1H, m), 1.82 (1H, m), 1.66 (2H, m), 1.52 (1H,
m), 1.39 (1H, m), 1.17 (13H, m). 13C NMR 155.8, 155.3,
149.8, 135.1, 122.8, 111.9, 110.7, 69.9 (d, 2Jˆ5.9 Hz), 25.5
(d, 1Jˆ139.6 Hz), 25.2, 24.4 (d, 3Jˆ3.7 Hz), 18.1 (d,
2Jˆ20.9 Hz), 9.1. 31P NMR 30.22. ESI-MS (MeOH1NaCl)
813 (2M1Na, 36.8), 418 (M1Na, 100.0), 396 (M1H, 24.6).
28.9 (d, 1Jˆ130.0 Hz), 27.6, 16.8 (d, 2Jˆ21.2 Hz), 10.3. 31
P
NMR 22.8. ESI-MS (MeOH) 296 (M1H, 100.0). Anal.
Calcd for C11H14N5O3P´0.8H2O: C, 42.67; H, 5.08; N,
22.62; P, 10.00. Found: C, 42.56; H, 4.97; N, 22.70; P,
10.37.
Compound 38b was converted to the corresponding
E-isomer 38c by the same procedure. UV max (EtOH)
271 nm (1 11,700), 228 (1 25,200). H NMR (DMSO-d6)
1
4.1.23. (Z)- and (E)-2-Amino-6-chloro-9-[2-(diisopropyl-
phosphonoethyl)cyclopropylidene]ethyl]purine
(37b)
d 11.60 (1H, s), 8.92 (1H, s), 7.32 (1H, s), 7.21 (2H, brs),
4.50 (2H, m), 1.89 (1H, m), 1.80 (2H, m), 1.70 (1H, m), 1.53
(1H, m), 1.35 (1H, m), 1.19 (13H, m). 13C NMR 155.9,
155.1, 149.7, 134.7, 123.0, 111.2, 110.4, 69.9 (d, 2Jˆ
and (38b). A mixture of compound 36 (6.5 g, 16 mmol),
2-amino-6-chloropurine (4.06 g, 19.2 mmol) and Cs2CO3
(15.6 g, 48 mmol) in DMF (150 mL) was stirred at room
temperature for 4 h and then at 708C for 5 h. The solids
were ®ltered off and washed with DMF (2£30 mL). The
solvent was evaporated and the crude product was chroma-
tographed on a silica gel column (CH2Cl2/MeOHˆ40:1) to
1
2
6.6 Hz), 26.3, 26.1 (d, Jˆ139.6 Hz), 24.5, 16.3 (d, Jˆ
20.2 Hz), 11.4. 31P NMR 30.19. ESI-MS (MeOH1NaCl)
813 (2M1Na, 10.2), 418 (M1Na, 100.0), 396 (M1H,
23.4).

6058
H.-P. Guan et al. / Tetrahedron 58 (2002) 6047±6059
4.1.25. (Z)- and (E)-9-{[2-(Phosphonoethyl)cyclopropyl-
idene]methyl}guanine (17b) and (18b). The procedure
described for compounds 15b and 16b was followed.
Me3SiBr (0.95 mL, 7.2 mmol) was added dropwise to a
solution of compound 37c (474 mg, 1.2 mmol) in DMF
(40 mL) at 2408C. The crude product was puri®ed by chro-
matography on Dowex-1 as described for compound 15b to
give the Z-isomer 17b (242 mg, 65%). Mp.3508C
(decomp.). UV max (pH 7) 266 nm (1 12,900), 228 (1
(decomp.). UV max (pH 7) 291 nm (1 12,400), 228 (1
13,300), 199 (1 18,500). H NMR (sodium salt, D2O) d
1
7.96 (d, Jˆ7.6 Hz) and 7.80 (1H, d, Jˆ7.6 Hz, 1.8:1),
7.21 (s) and 7.05 (1H, s, 1.8:1), 6.01 (d, Jˆ7.2 Hz) and
5.95 (1H, d, Jˆ7.2 Hz, 1:1.8), 1.85 (m), 1.70 (m), 1.55
(m), 1.38 (m), 1.13 (m), 1.02 (m, total 7H). 13C NMR
166.3, 166.1, 157.3, 143.3, 142.8, 121.1, 120.3, 115.1,
114.6, 96.5, 96.1, 28.4 (2 overlapped d, 1Jˆ137.0 Hz),
2
2
27.5, 27.0, 18.0 d, Jˆ20.7 Hz), 15.4 (d, Jˆ22.2 Hz), 9.6,
7.4. 31P NMR 24.2, 23.8. ESI-MS (NaCl) 316 (M12Na2H,
294 (M1Na, 100.0), 272 (M1H, 88.9). Anal. Calcd for
C10H14N3O4P: C, 44.29; H, 5.20; N, 15.49; P, 11.42.
Found: C, 44.35; H, 5.40; N, 15.28; P, 11.61.
1
30,800). H NMR (sodium salt, D2O) d 7.88 (1H, s), 6.91
(1H, s), 1.95 (1H, m), 1.86 (1H, m), 1.43 (3H, m), 1.27 (1H,
m), 1.08 (1H, t, Jˆ6.4 Hz). 13C NMR 163.2, 157.3, 149.9,
1
136.4, 116.3, 121.1, 109.3, 28.3 (d, Jˆ130.0 Hz), 26.9,
18.3 (d, 3Jˆ20.2 Hz), 8.1. 31P NMR 22.7. ESI-MS
(MeOH1NaCl) 334 (M1Na, 27.4), 312 (M1H, 25.0),
100 (100.0). Anal. Calcd for C11H14N5O4P´0.3H2O: C,
41.73; H, 4.65; N, 22.12; P, 9.78. Found: C, 42.02; H,
4.96; N, 21.82; P, 10.04.
Acknowledgements
Our thanks are due to Dr Lew M. Hrihorczuk, Central
Instrumentation Facility, Department of Chemistry,
Wayne State University, for mass spectra. The work
described herein was supported by US Public Health
Service Grant RO1-CA32779 (J. Z.) from the National
Cancer Institute and Contract NO1-AI85347 (E. R. K.)
from the National Institute of Allergy and Infectious
Diseases, National Institutes of Health, Bethesda, MD.
The E-isomer 18b (475 mg, 67%) was obtained following a
similar procedure from compound 38c (900 mg,
2.28 mmol). Mp.3508C (decomp.). UV max (pH 7)
266 nm (1 12,400), 229 (1 32,400). 1H NMR (sodium
salt, D2O) d 7.81 (1H, s), 6.89 (1H, s), 1.75 (1H, m), 1.66
(3H, m), 1.52 (2H, m), 1.15 (1H, m). 13C NMR 158.3, 153.6,
149.2, 135.6, 115.2, 119.5, 108.8, 28.1 (d, Jˆ131.8 Hz),
3
27.0, 16.2 (d, Jˆ20.5 Hz), 10.6. 31P NMR 25.7. ESI-MS
(MeOH1NaCl) 334 (M1Na, 36.9), 311 (M1H, 33.9), 100
(100.0). Anal. Calcd for C11H14N5O4P: C, 42.45; H, 4.53; N,
22.50; P, 9.95. Found: C, 42.22; H, 4.72; N, 22.31; P, 10.07.
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4.1.26. (Z1E)-9-{[2-(Diisopropylphosphonoethyl)cyclo-
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A
stirred
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(d, Jˆ3.0 Hz), 69.8 (d, Jˆ5.9 Hz), 26.6 (d, Jˆ3.4 Hz),
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